Induction of fibroblast growth factor 10 (FGF10) in the ileal crypt epithelium after massive small bowel resection suggests a role for FGF10 in gut adaptation

Posttranscriptional Regulation of Intestinal Mucosal Growth and Adaptation by Noncoding RNAs in Critical Surgical Disorders

The human intestinal epithelium has an impressive ability to respond to insults and its homeostasis is maintained by well-regulated mechanisms under various pathophysiological conditions. Nonetheless, acute injury and inhibited regeneration of the intestinal epithelium occur commonly in critically ill surgical patients, leading to the translocation of luminal toxic substances and bacteria to the bloodstream. Effective therapies for the preservation of intestinal epithelial integrity and for the prevention of mucosal hemorrhage and gut barrier dysfunction are limited, primarily because of a poor understanding of the mechanisms underlying mucosal disruption. Noncoding RNAs (ncRNAs), which include microRNAs (miRNAs), long ncRNAs (lncRNAs), circular RNAs (circRNAs), and small vault RNAs (vtRNAs), modulate a wide array of biological functions and have been identified as orchestrators of intestinal epithelial homeostasis. Here, we feature the roles of many important ncRNAs in controlling intestinal mucosal growth, barrier function, and repair after injury-particularly in the context of postoperative recovery from bowel surgery. We review recent literature surrounding the relationships between lncRNAs, microRNAs, and RNA-binding proteins and how their interactions impact cell survival, proliferation, migration, and cell-to-cell interactions in the intestinal epithelium. With advancing knowledge of ncRNA biology and growing recognition of the importance of ncRNAs in maintaining the intestinal epithelial integrity, ncRNAs provide novel therapeutic targets for treatments to preserve the gut epithelium in individuals suffering from critical surgical disorders.

Roles of the fibroblast growth factor signal transduction system in tissue injury repair

Following injury, tissue autonomously initiates a complex repair process, resulting in either partial recovery or regeneration of tissue architecture and function in most organisms. Both the repair and regeneration processes are highly coordinated by a hierarchy of interplay among signal transduction pathways initiated by different growth factors, cytokines and other signaling molecules under normal conditions. However, under chronic traumatic or pathological conditions, the reparative or regenerative process of most tissues in different organs can lose control to different extents, leading to random, incomplete or even flawed cell and tissue reconstitution and thus often partial restoration of the original structure and function, accompanied by the development of fibrosis, scarring or even pathogenesis that could cause organ failure and death of the organism. Ample evidence suggests that the various combinatorial fibroblast growth factor (FGF) and receptor signal transduction systems play prominent roles in injury repair and the remodeling of adult tissues in addition to embryonic development and regulation of metabolic homeostasis. In this review, we attempt to provide a brief update on our current understanding of the roles, the underlying mechanisms and clinical application of FGFs in tissue injury repair.

Role of FGF10/FGFR2b Signaling in Mouse Digestive Tract Development, Repair and Regeneration Following Injury

During embryonic development, the rudimentary digestive tract is initially a tube-like structure. It is composed of epithelial cells surrounded by mesenchymal cells. Reciprocal epithelial–mesenchymal interactions progressively subdivide this primitive tube into distinct functional regions: the tongue, the pharynx, the esophagus, the stomach, the duodenum, the small intestine, the cecum, the large intestine, the colon, and the anus as well as the pancreas and the liver. Fibroblast growth factors (Fgfs) constitute a family of conserved small proteins playing crucial roles during organogenesis, homeostasis, and repair after injury. Among them, fibroblast growth factor 10 (Fgf10) has been reported to orchestrate epithelial–mesenchymal interactions during digestive tract development. In mice, loss of function of Fgf10 as well as its receptor fibroblast growth factor receptor 2b (Fgfr2b) lead to defective taste papillae in the tongue, underdeveloped and defective differentiation of the stomach, duodenal, cecal, and colonic atresias, anorectal malformation, as well as underdeveloped pancreas and liver. Fgf signaling through Fgfr2b receptor is also critical for the repair process after gut injury. In the adult mice, a malabsorption disorder called small bowel syndrome is triggered after massive small bowel resection (SBR). In wild-type mice, SBR leads to a regenerative process called gut adaptation characterized by an increase in the diameter of the remaining small intestine as well as by the presence of deeper crypts and longer villi, altogether leading to increased intestinal surface. Intestinal stem cells are key for this regeneration process. Induction of Fgf10 expression in the Paneth cells located in the crypt following SBR suggests a critical role for this growth factor in the process of gut adaptation.

Fibroblast Growth Factors in the Gastrointestinal Tract: Twists and Turns

Fibroblast growth factors (FGFs) are a family of conserved peptides that play an important role in the development, homeostasis, and repair processes of many organ systems, including the gastrointestinal tract. All four FGF receptors and several FGF ligands are present in the intestine. They play important roles in controlling cell proliferation, differentiation, epithelial cell restitution, and stem cell maintenance. Several FGFs have also been proven to be protective against gastrointestinal diseases such as inflammatory bowel diseases or to aid in regeneration after intestinal loss associated with short bowel syndrome. Herein, we review the multifaceted actions of canonical FGFs in intestinal development, homeostasis, and repair in rodents and humans. Developmental Dynamics 246:344-352, 2017. © 2016 Wiley Periodicals, Inc.

Role of fibroblast growth factors in organ regeneration and repair

In its broad sense, regeneration refers to the renewal of lost cells, tissues or organs as part of the normal life cycle (skin, hair, endometrium etc.) or as part of an adaptive mechanism that organisms have developed throughout evolution. For example, worms, starfish and amphibians have developed remarkable regenerative capabilities allowing them to voluntarily shed body parts, in a process called autotomy, only to replace the lost parts afterwards. The bizarre myth of the fireproof homicidal salamander that can survive fire and poison apple trees has persisted until the 20th century. Salamanders possess one of the most robust regenerative machineries in vertebrates and attempting to draw lessons from limb regeneration in these animals and extrapolate the knowledge to mammals is a never-ending endeavor. Fibroblast growth factors are potent morphogens and mitogens that are highly conserved among the animal kingdom. These growth factors play key roles in organogenesis during embryonic development as well as homeostatic balance during postnatal life. In this review, we provide a summary about the current knowledge regarding the involvement of fibroblast growth factor signaling in organ regeneration and repair. We also shed light on the use of these growth factors in previous and current clinical trials in a wide array of human diseases.

Therapeutic efficacy of fibroblast growth factor 10 in a rabbit model of dry eye

The aim of the present study was to investigate the therapeutic efficacy of fibroblast growth factor 10 (FGF10) in the promotion of healing, survival and expression of mucin in corneal epithelial cells in a rabbit dry eye model. A total of 12 healthy female New Zealand white rabbits were divided randomly into three groups. The lacrimal glands were injected with saline either alone (normal control group) or with concanavalin A (Con A), with either topical phosphate-buffered saline (PBS; PBS control group) or 25 µg/ml FGF10 (FGF10 treatment group). Lacrimal gland inflammation, tear function, corneal epithelial cell integrity, cell apoptosis and mucin expression were subsequently assessed. Lacrimal gland tissue biopsies were performed in conjunction with histology and electron microscopy observations. Tear meniscus height (TMH) and tear meniscus area (TMA) were measured using Fourier domain-optical coherence tomography. Tear membrane break-up time (TBUT) was also assessed and corneal fluorescein staining was performed. The percentages of apoptotic corneal and conjunctival (Cj) epithelial cells (ECs) were counted using a terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method. The mRNA expression levels of Muc1 were determined using reverse transcription-quantitative polymerase chain reaction analyses. The TMH and TMA values of the PBS and treatment groups were found to be significantly reduced, compared with those of the normal control group 3 days after Con A injection. However, the TMH and TMA of the FGF10 treatment group were higher, compared with those of the PBS group 3 and 7 days after treatment, respectively. Furthermore, the FGF10 treatment group exhibited prolonged TBUT, reduced corneal fluorescein staining and repaired epithelial cell ultra-structure7 days after treatment. The percentages of apoptotic corneal- and Cj-ECs in the FGF10 treatment group were significantly reduced, compared with those in the PBS group. FGF10 significantly induced the mRNA expression of Muc1 in the corneal epithelial cells, compared with the normal control group, and induced higher mRNA expression levels of Muc1 in the Cj-ECs, compared with the PBS control group. In the present study, the rabbit dry eye model was successfully established 3 days after lacrimal gland Con A injection. FGF10 eye drops increased TMH and TMA, promoted corneal epithelial healing, reduced apoptosis of the corneal- and Cj-ECs and led to increased expression of Muc1.

Fibroblast growth factor 10 alters the balance between goblet and Paneth cells in the adult mouse small intestine

Intestinal epithelial cell renewal relies on the right balance of epithelial cell migration, proliferation, differentiation, and apoptosis. Intestinal epithelial cells consist of absorptive and secretory lineage. The latter is comprised of goblet, Paneth, and enteroendocrine cells. Fibroblast growth factor 10 (FGF10) plays a central role in epithelial cell proliferation, survival, and differentiation in several organs. The expression pattern of FGF10 and its receptors in both human and mouse intestine and their role in small intestine have yet to be investigated. First, we analyzed the expression of FGF10, FGFR1, and FGFR2, in the human ileum and throughout the adult mouse small intestine. We found that FGF10, FGFR1b, and FGFR2b are expressed in the human ileum as well as in the mouse small intestine. We then used transgenic mouse models to overexpress Fgf10 and a soluble form of Fgfr2b, to study the impact of gain or loss of Fgf signaling in the adult small intestine. We demonstrated that overexpression of Fgf10 in vivo and in vitro induces goblet cell differentiation while decreasing Paneth cells. Moreover, FGF10 decreases stem cell markers such as Lgr5, Lrig1, Hopx, Ascl2, and Sox9. FGF10 inhibited Hes1 expression in vitro, suggesting that FGF10 induces goblet cell differentiation likely through the inhibition of Notch signaling. Interestingly, Fgf10 overexpression for 3 days in vivo and in vitro increased the number of Mmp7/Muc2 double-positive cells, suggesting that goblet cells replace Paneth cells. Further studies are needed to determine the mechanism by which Fgf10 alters cell differentiation in the small intestine.

Stem cells and biopharmaceuticals: vital roles in the growth of tissue-engineered small intestine

Tissue engineering currently constitutes a complex, multidisciplinary field exploring ideal sources of cells in combination with scaffolds or delivery systems in order to form a new, functional organ to replace native organ lack or loss. Short bowel syndrome (SBS) is a life-threatening condition with high morbidity and mortality rates in children. Current therapeutic strategies consist of costly and risky allotransplants that demand lifelong immunosuppression. A promising alternative is the implantation of autologous organoid units (OU) to create a tissue-engineered small intestine (TESI). This strategy is proven to be stem cell and mesenchyme dependent. Intestinal stem cells (ISCs) are located at the base of the crypt and are responsible for repopulating the cycling mucosa up to the villus tip. The stem cell niche governs the biology of ISCs and, together with the rest of the epithelium, communicates with the underlying mesenchyme to sustain intestinal homeostasis. Biopharmaceuticals are broadly used in the clinic to activate or enhance known signaling pathways and may greatly contribute to the development of a full-thickness intestine by increasing mucosal surface area, improving blood supply, and determining stem cell fate. This review will focus on tissue engineering as a means of building the new small intestine, highlighting the importance of stem cells and recombinant peptide growth factors as biopharmaceuticals.

Fgf10 overexpression enhances the formation of tissue-engineered small intestine

Short bowel syndrome (SBS) is a morbid and mortal condition characterized in most patients by insufficient intestinal surface area. Current management strategies are inadequate, but tissue-engineered small intestine (TESI) offers a potential therapy. A barrier to translation of TESI is the generation of scalable mucosal surface area to significantly increase nutritional absorption. Fibroblast growth factor 10 (Fgf10) is a critical growth factor essential for the development of the gastrointestinal tract. We hypothesized that overexpression of Fgf10 would improve the generation of TESI. Organoid units, the multicellular donor tissue that forms TESI, were derived from Rosa26(rtTA/+), tet(o)Fgf10/(-) or Fgf10(Mlc-nlacZ-v24) (hereafter called Fgf10(lacZ)) mice. These were implanted into the omentum of NOD/SCID γ-chain-deficient mice and induced with doxycycline in the case of tet(o)Fgf10/(-). Resulting TESI were explanted at 4 weeks and studied by histology, quantitative RT-PCR and immunofluorescence. Four weeks after implantation, Fgf10 overexpressing TESI was larger and weighed more than the control tissues. Within the mucosa, the villus height was significantly longer and crypts contained a greater percentage of proliferating epithelial cells. A fully differentiated intestinal epithelium with enterocytes, goblet cells, enteroendocrine cells and Paneth cells was identified in the Fgf10-overexpressing TESI, comparable to native small intestine. β-Galactosidase expression was found in both the epithelium and the mesenchyme of the TESI derived from the Fgf10(LacZ) duodenum. However, this was not the case with TESI generated from jejunum and ileum. We conclude that Fgf10 enhances the formation of TESI.

Fibroblast growth factor 10-fibroblast growth factor receptor 2b mediated signaling is not required for adult glandular stomach homeostasis

The signaling pathways that are essential for gastric organogenesis have been studied in some detail; however, those that regulate the maintenance of the gastric epithelium during adult homeostasis remain unclear. In this study, we investigated the role of Fibroblast growth factor 10 (FGF10) and its main receptor, Fibroblast growth factor receptor 2b (FGFR2b), in adult glandular stomach homeostasis. We first showed that mouse adult glandular stomach expressed Fgf10, its receptors, Fgfr1b and Fgfr2b, and most of the other FGFR2b ligands (Fgf1, Fgf7, Fgf22) except for Fgf3 and Fgf20. Fgf10 expression was mesenchymal whereas FGFR1 and FGFR2 expression were mostly epithelial. Studying double transgenic mice that allow inducible overexpression of Fgf10 in adult mice, we showed that Fgf10 overexpression in normal adult glandular stomach increased epithelial proliferation, drove mucous neck cell differentiation, and reduced parietal and chief cell differentiation. Although a similar phenotype can be associated with the development of metaplasia, we found that Fgf10 overexpression for a short duration does not cause metaplasia. Finally, investigating double transgenic mice that allow the expression of a soluble form of Fgfr2b, FGF10's main receptor, which acts as a dominant negative, we found no significant changes in gastric epithelial proliferation or differentiation in the mutants. Our work provides evidence, for the first time, that the FGF10-FGFR2b signaling pathway is not required for epithelial proliferation and differentiation during adult glandular stomach homeostasis.

Smooth muscle adaptation and recovery of contractility after massive small bowel resection in rats

Previous studies have suggested that massive small bowel resection (mSBR) compromises the normal intestinal processes of digestion and absorption, and requires an adaptive response to regain full function and reinstate coordinated contractile activity of the circular smooth muscle. This study was designed to investigate spontaneous contractile activity of circular smooth muscle using the mSBR rat model and to determine the functional role of M(2) and M(3) muscarinic acetylcholine receptors (mAChR) in this process. Male Sprague-Dawley rats underwent an 80% proximal SBR or sham operation. Markers of adaptation, including villus and microvillus height, were analyzed by hematoxylin and eosin staining and transmission electron microscopy. Contractility was measured by attaching the distal ileum strips to strain gauge transducers and exposing the tissue to varying doses of the cholinergic agonist carbachol. Protein expressions of M(2)- and M(3)-mAChR in intestinal smooth muscle (ISM) were detected by Western blot. Following mSBR, the ISM showed perturbed spontaneous rhythmic contraction, irregular amplitude and slow frequency by muscle strip test. However, by two weeks after mSBR, the contractile function of circular smooth muscle was found to have returned to normal levels. Protein expression of M(2)-mAChR was down-regulated following mSBR but up-regulated during the adaptive process when contractile activity of circular smooth muscle was regained. These results indicate that smooth muscle contractility was spontaneously restored in rats following mSBR, and involved the acetylcholine receptors M(2) and M(3). Thus, the disrupted contractile response of smooth muscle in short bowel syndrome may be corrected by therapeutic intervention to restore the expressions of M(2)- and M(3)-mAChR to pre-mSBR levels.

Oral administration of Enterococcus faecalis EC-12 cell preparation improves villous atrophy after weaning through enhancement of growth factor expression in mice

Lactic acid bacteria, either alive or dead, can improve villous atrophy caused by weaning in both piglets and mice. In this experiment, we tried to detect the molecules involved in this phenomenon with a real-time RT-PCR array approach. Weaning pups of mice were administered either a suspension of an Enterococcus faecalis EC-12 dried cell preparation (EC-12) or saline for 11 consecutive days after weaning. The jejunal and ileal villous heights were measured histologically, and the expression levels of 86 genes were analyzed for the jejunal and ileal epithelial cells and the lamina propria (LP). EC-12 induced significantly higher villous height in the jejunum and the ileum. Interleukin (IL)-6, fibroblast growth factor (FGF)-7, -10, and -22, and the platelet-derived growth factor (PDGF) beta in the jejunal and the ileal LP were the most enhanced genes by EC-12. The possible role of these molecules in the improvement of villous atrophy is discussed.